The present invention relates to an apparatus and method for augmenting cardiac function.
There is general agreement within the medical profession that there is a growing epidemic of heart failure in the western world. In the United States of America, heart failure is directly implicated in approximately a quarter of a million deaths per year. With survival times after initial problems typically of one and a half years for men and two and a half years for women, severe heart failure has a worse outlook than many types of cancer.
Mechanical circulatory support systems have been proposed in the past. Details of such systems are described in Curr Probi Cardiol, December 1998, pages 726-764. The known devices range from the intraaortic balloon pump which has been used extensively and comprises an inflatable balloon inserted into the left ventricular cavity, the balloon being cyclically inflated and deflated so as to assist blood displacement into the aorta, to total cardiac replacement systems. Heart replacement systems are not yet developed to an extent which makes them suitable for general use. Even relatively less invasive procedures such as the intraaortic balloon pump exhibit disadvantages, not least problems with maintaining effectiveness over prolonged periods given the introduction into the vascular system of components with relatively large surface areas.
A proposal has also been made to improve cardiac function by providing a balloon device which is interposed between the myocardium and the pericardium. The inserted balloon device is inflated in synchronism with the normal heartbeat so as to squeeze the left ventricle of the heart as blood is being displaced into the aorta as a result of normal heart function. Thus this device assists normal heart function. One of the problems with such an arrangement however is that the inflation volume of the balloon must be very much larger than the resultant reduction in volume of the left ventricular cavity. This is because the pericardium is itself not a rigid structure and therefore some of the expansion of the balloon is absorbed by expansion of the pericardium. In addition expansion of a balloon in the pericardium will push blood from the atria back into their respective veins absorbing a considerable amount of the expansion of the balloon and impairing cardiac filling. Thus an increase in blood delivery of only 20 ml per beat may require a balloon displacement of say 100 ml. The system is thus not efficient and demands more power than can readily be made available in portable subcutaneous form.
It has been proposed in for example U.S. Pat. No. 6,050,936 to treat a failing heart by reducing tension in the myocardial wall of the heart. Tension members are arranged to extend across the left and right ventricles of the heart, the tension members being anchored to the myocardial wall so as to pull the myocardial wall inwards adjacent areas of anchorage. This improves heart function but is essentially a static arrangement. There is no suggestion that the spacing between the points of anchorage of the tension members should be adjusted cyclically for instance in synchronism with the natural heartbeat cycle.
Xenotransplantation has been proposed in which genetically altered animal hearts are implanted into humans. One of the problems with this approach is rejection. The process of rejection starts with the immune system detecting that a piece of tissue is not identical to that of the body""s other tissues and subsequently attacking it. All humans have essentially unique antigenic characteristics so, for an animal generally heart to be implanted and not recognised as foreign, it would have to precisely match the antigenic characteristics of that human. Such animals cannot be produced in advance of the requirement for such a heart. It has been proposed to raise animals that are fairly close in antigenic characteristics to several groups of potential human recipients but as an exact match cannot be achieved immunosuppressive drugs are still required, the use of such drugs carrying with them the risk of infection without totally avoiding the risk of rejection. Still further problem with xenotransplantation is the possibility that the transplanted heart may harbour an animal virus that when combined with a human virus in the recipient may lead to a particularly virulent form of infection. In addition the longevity of animal organs is not known, for instance pigs do not live for 80 years as humans can.
It is an object of the present invention to obviate or mitigate the problems outlined above.
According to the present invention there is provided an apparatus for augmenting cardiac function, comprising means for cyclically modifying dimensional characteristics of a heart, the modifying means comprising a linkage extending between at least two points on the myocardium of the heart, and means for controlling the length of the linkage to control the spacing between the said at least two points on the myocardium.
The invention also provides a method for augmenting cardiac function, wherein dimensional characteristics of a heart are modified cyclically, the dimensional characteristics being modified by engaging a linkage between at least two points on the myocardium of the heart, and cyclically modifying the length of the linkage to control the spacing between the said at least two points on the myocardium.
The invention essentially provides a device which is attached to or impinges on the myocardium at two or more points and alters the relative distance between those points in a manner designed to increase cardiac output. The device can be endovascularly placed, or percutaneously placed under local anaesthetic.
Preferably, means are provided for sensing the beating of the heart, and means are provided for controlling the length of the linkage in synchronism with the sensed heartbeats. The ratio of the number of heartbeats to the number of cyclical modifications to the dimensional characteristics may be selectively adjusted.
Preferably, the linkage is adapted to traverse the left ventricular cavity. The linkage may comprise means for attachment to the at least two points on the myocardium of the heart, and means for applying tension to a member such as a cable extending between the points of attachments.
The cable may extend from one end of a sheath, the distal end of the cable being provided with means for attachment to a first point on the myocardium, and the end of the sheath from which the cable projects being adapted to bear against a second point of the myocardium, the linkage control means being adapted to control the length of cable extending from the sheath. The cable may comprise two or more cables each received within a common sheath, the distal ends of the two cables being provided with means for attachment to separate points on the myocardium, or the cable may branch into two or more sub-cables each adapted to be connected to a separate point on the myocardium.
In an alternative arrangement, a tension applying means may be arranged between a first element for attachment to one point on the myocardium and a second element for attachment to a second point on the myocardium, to adjust the spacing between the first and second elements. The tension applying means may comprise a piston and cylinder arrangement, the cylinder of the arrangement being attached to one element and the piston of the arrangement being attached to the other element.
The apparatus may be normally quiescent, but comprise means for detecting cardiac arrest, and means for initiating cyclical modification of the dimensional characteristics in response to detection of cardiac arrest.
The invention may also provide a surgical procedure for installing a left ventricular assist device to augment cardiac function, wherein a cable is inserted into the heart to traverse the left ventricular cavity, the distal end of the cable is attached to the myocardium of the heart, a sheath through which the cable extends is positioned such that the distal end of the sheath bears against the myocardium at a point spaced from the distal end of the cable, and an actuator is connected to the cable, and an actuator is connected to the cable and sheath to enable control of the spacing between the distal ends of the cable and sheath.
The invention further provides a surgical procedure for installing a left ventricular assist device to augment cardiac function, wherein at least one linkage is connected between at least two points of attachment to the myocardium adjacent the left ventricular cavity, the linkage containing a device for controlling the length of the linkage between the points of attachment, and the control device is connected to an actuator adapted to control the spacing between the points of attachment.